front
1.in front of作“在…的前面”解。例如：There is a hill in front of the house. in the front of作“在…的前部”解。例如：An artist's family live in the front of the house. 可以说The boy is sitting in front of the girl，不可说The boy is sitting in the front of the girl。也不可说The boy is sitting in the girl's front。
at the front of作“在…的前面近处”或“在…的前端”解。例如：There is a big tree at the front of the house. 和There are two doors at the front of the house.
2.front作“（战场）前线”解时前面用on或at都可以，但production front（生产战线），cultural front（文化战线）等前面习惯用on。
